personally, ive read books, and done tutorials - the whole 9 trying to fully understand PHP. variables, arrays, functions, conditional statements - database integration. There IS common ground with most languages, and if you've dabbled back in the day, it is pretty simple to pickup.
but what i found worked for me is that I found a project that interested ME that I built from the ground up using php/sql. Between troubleshooting broken code, utilizing correct syntax/form, and generating the fastest queries to my DB, I learned how to build an outstanding web app - and ALSO learned php better than any of those tutorials/books ever read me.